First of all, welcome to the site. I'm no expert, but there are LOTS of members who are. I have 2 girls, 7 1/2 mos. old, so I'm rather new to this breed. But I think you're doing the right thing, changing him off Purina and to a good quality food. I also think you should absolutely get him into the vet. I would be surprised if it's his food change, but then I've seen food allergies do some crazy things (not me personally, but with other members). Do you use vitamins at all? NuVet Plus is an excellent multi vitamin, I use it every day with Gertie and Ida. They also have a supplement for hips. Their website is nuvet.com Hope you get good news at the vet.